CHAPTER III 



The Shore and its Plant and Animal Associations 



It has already been pointed out that, whereas the fauna 

 extends to the greatest known depths, the vegetation of 

 the sea is definitely limited to the surface and shallow 

 waters. In contrast to the deeper waters, therefore, we 

 find that the shore presents the same typical combination 

 and interaction of plant and animal as is seen on land, 

 except that life here functions in both media, air and 

 water, by turns. The life factors are thus duplicated. In 

 passing from entirely land to purely marine conditions, we 

 traverse this region, which may be considered as a region of 

 fluctuation and of evolution ; a region wherein are to be 

 found the most complex conditions of the whole globe. 



We have firstly the upper limits of sea action, the zone 

 only reached by spring tides ; next, the typical shore zone 

 lying between the high and low water marks of ordinary 

 tides ; below that, a zone only exposed during low spring 

 tides : these make up the shore. Below it we have a region 

 which, although still affected by some of the conditions of 

 stress (wave action, etc.) found on the shore, nevertheless 

 contains vegetation and enjoys abundant light ; tidal 

 phenomena are eliminated. As we proceed seaward we 

 gradually eliminate two further factors of importance, namely, 

 wave action and light. With the latter, plant life is also 

 eliminated, with all that it means to animals, while the absence 

 of wave action frees the fauna from another (generally 

 adverse) set of factors. We thus get a simplification of the 

 environmental factors as compared with the land fauna, 

 and especially with that of the shore. The shore, then, is 



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